A wireless local area network (LAN) system in compliance with the IEEE 802.11 standard has been improved in throughout every year, and have come into widespread use as one principle wireless access. Because the wireless LAN system can use an unlicensed band that is a frequency band which does not require a license, various types of wireless terminals/stations have come into widespread use. Because random access control that uses a CSMA/CA method is performed on wireless communication in the unlicensed band, a hidden wireless station problem remains a major obstacle.
The hidden wireless station problem is a problem that occurs when transmission signals of wireless stations which do not mutually perform a carrier sensing function collide with each other, thereby making a throughput characteristic worse. As a method of solving the problem, for example, a flow control that uses Request-To-Send (RTS)/Clear-To-Send (CTS) has been proposed. When it comes to exchange of an RTS frame and a CTS frame, even in a case where a wireless signal from a transmission station, which cannot be detected, is present in the reception station, the reception station configures a NAV using the CTS frame in response to the RTS frame from the transmission station, and thus the hidden wireless station problem can be solved, thereby preventing the throughput characteristic from being made worse.
Incidentally, in some cases, in the reception station that can detect a wireless signal that is transmitted by each of the hidden wireless stations, an exposed situation in reception occurs in which a normal reception rate of a desired wireless signal decreases due to exposure from the wireless signal. Incidentally, in some cases, in the transmission station that can detect the wireless signal that is transmitted by each of the hidden wireless stations, an exposed situation in transmission occurs in which a transmission opportunity acquisition rate for transmitting the wireless signal from the wireless station itself decreases due to exposure from the wireless signal.
However, also in some cases, a primary cause of the decrease in the normal reception rate of the reception station is that transmission timings of a plurality of transmission stations overlap while random access control that uses the CSMA/CA method is performed. Furthermore, also in some cases, a primary cause of the decrease in the transmission opportunity acquisition rate of the transmission station is that there are many wireless stations that perform the random access control that uses the CSMA/CA method. The details will be described below.
Therefore, there is a need to accurately determine the exposed situation in reception in which the normal reception rate decreases and the exposed situation in transmission in which the transmission opportunity acquisition rate decreases, to reflect a result of the determination in the access control by the transmission station and the reception station, and to improve the throughput characteristic.
Patent Document 1 discloses a method in which comparison is made between a BSS ID that is detected in an access point and a BSS ID that is detected in a station, in which the risk of packet collision is determined, and in which the decrease in throughput due to the hidden wireless station problem or an exposed wireless station problem is evaluated from the stored tendency of traffic in the access point.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2015-115667